1. Field of the Invention
The present invention relates to a heat dissipating fan and, more particularly, to a small sized heat dissipating fan including a speed adjuster to adjust rotational speed of the small sized heat dissipating fan.
2. Description of the Related Art
Referring to FIG. 1, a conventional small sized heat dissipating fan is shown. The conventional small sized heat dissipating fan includes a housing 7, a stator 8 and a rotor 9, with the housing 7 receiving the stator 8 and the rotor 9. The housing 7 has a base 71 where the stator 8 and the rotor 9 are mounted. The stator 8 fixed to the base 71 has a magnetizing member 81 with a plurality of windings 811 and a circuit board 82 electrically connecting to the windings 811, such that a rated voltage provided by a power supply can generate a current passing through the winding 811 to generate alternating magnetic fields. The rotor 9 has a shaft 91, an impeller 92 and a magnet 93. One end of the shaft 91 is fixed to the center of the impeller 92 and the other end of the shaft 91 extends through the magnetizing member 81, with the shaft 91 being rotatably coupled to the stator 8. The magnet 93 is mounted to an inner surface of the impeller 92 and faces the magnetizing member 81 of the stator 8 to react with the alternating magnetic fields generated from the windings 811, so that the rotor 9 can be driven to rotate relative to the stator 8. In general, the rotor 9 of the conventional small sized heat dissipating fan is driven to rotate by the current through the windings 811 from the rated voltage via the circuit board 82. Therefore, the rotor 9 rotates at a fixed rated rotational speed after being actuated.
However, when a need for decreasing the rated rotational speed is required, turns of the windings 811 of the magnetizing member 81 should be changed or the circuit board 82 should be replaced with another circuit board providing a rated voltage smaller than that of the circuit board 82. In order to produce the conventional small sized heat dissipating fans of various rated rotational speeds, a manufacturer of the conventional small sized heat dissipating fan has to make a large quantity of the magnetizing members 81 or circuit boards 82 of various kinds. As a result, the production cost can not be reduced, and there may be a risk of slow selling. Hence, there is a need for an improvement over the conventional small sized heat dissipating fan.